Revert of Revert of Return GrGLContext from GrTestTarget

src/gpu/GrGpu.h

Index: src/gpu/GrGpu.h
diff --git a/src/gpu/GrGpu.h b/src/gpu/GrGpu.h
index d9c2e18bdb1070548500de3484ab8060886c29b6..dc6e9c0df6c46d49e05b798e5edc4a0c65350005 100644
--- a/src/gpu/GrGpu.h
+++ b/src/gpu/GrGpu.h
@@ -17,7 +17,7 @@
 
 class GrBatchTracker;
 class GrContext;
-struct GrGLInterface;
+class GrGLContext;
 class GrIndexBuffer;
 class GrNonInstancedVertices;
 class GrPath;
@@ -365,7 +365,7 @@
     bool attachStencilAttachmentToRenderTarget(GrRenderTarget* target);
 
     // This is only to be used in tests.
-    virtual const GrGLInterface* glInterfaceForTesting() const { return NULL; }
+    virtual const GrGLContext* glContextForTesting() const { return NULL; }
 
 protected:
     // Functions used to map clip-respecting stencil tests into normal